2n = 14 (U. reptans) or 28 or 30 or 36 or 42 or 44 or 48, commonly adventive.

Habitat. Mesophytic. Savanna, often weedy. Shade species, or species of open habitats (usually).

Classification. Panicoideae; Paniceae.

Notes. The genus is defined by the abaxial orientation of its spikelets, with which is associated a plano-convex shape, cuspidate tip and mucronate upper lemma. When the spikelets are paired their orientation becomes ambiguous and diagnosis then rests upon their facies. Unfortunately orientation and facies are not wholly correlated, some intermediates being noted under Brachiaria, and it is a moot point whether generic rank is justified (Clayton and Renvoize, 1986). A number of agrostologists (Webster, 1987; Macfarlane, 1992; Jacobs and Wall, 1993; Morrone and Zuloaga, 1993) have united the two genera (excluding Brachiaria eruciformis), but I feel this step is premature pending detailed cladistic work of all species (BKS).